Stereoscopic image apparatus

ABSTRACT

A stereoscopic image apparatus that is capable of minimizing loss of optical energy and improving quality of a stereoscopic image is disclosed. The stereoscopic image apparatus includes a polarizing beam splitter to reflect or transmit incident light based on polarization components of the light to split the light in at least three different directions, a reflective member to reflect the light reflected by the polarizing beam splitter to a screen, at least one modulator to modulate the light reflected by the reflective member and the light transmitted through the polarizing beam splitter, and a refractive member disposed in an advancing direction of light to be incident upon the polarizing beam splitter to refract the light to be incident upon the polarizing beam splitter.

TECHNICAL FIELD

The present invention relates to a stereoscopic image apparatus that iscapable of transmitting some of light constituted by an incident imagesignal and reflecting the rest of the light to split the light andcondensing the split light on a screen to increase brightness.

BACKGROUND ART

FIG. 1 is a view showing a conventional polarizing beam splitter.

When light having a P-polarization and an S-polarization in a mixedstate is incident upon a polarizing beam splitter (PBS) 1, theP-polarization is transmitted through the polarizing beam splitter 1 andthe S-polarization is reflected by the polarizing beam splitter 1.

The reflected S-polarization and the transmitted P-polarization aredirected in the same direction by diamond-shaped prisms 2 and 3.

For example, the P-polarization is transmitted through the prism and isthen changed into an S-polarization by a half wave plate (retarder) 4.

As a result, the light having the P-polarization and the S-polarizationin the mixed state is changed into the same polarization, e.g. theS-polarization, by the polarizing beam splitter. That is, the lighthaving the P-polarization and the S-polarization in the mixed state hasthe same direction.

An operation principle of a stereoscopic image apparatus using theconventional polarizing beam splitter is as follows. U.S. Pat. No.7,857,455 is referred to.

As shown in FIG. 2, light emitted from an image surface 5 generating animage in a projector passes through a projection lens 6 and is thensplit into two beams by a polarizing beam splitter 7.

That is, light having an S-polarization state and a P-polarization stateis reflected by the polarizing beam splitter 7 or transmitted throughthe polarizing beam splitter 7.

The transmitted or reflected P-polarization component is changed intoS-polarization while passing through a half wave retarder 8. TheS-polarization is concentrated on a projection screen via reflectivemembers 9 and 10, a polarizer 11, and a modulator 12.

The modulator 12 may change a polarization state/direction, for example,according to an electric signal.

On the ether hand, the S-polarization component reflected by thepolarizing beam splitter 7 reaches the projection screen via areflective member 13 in a state in which the S-polarization ismaintained in the same-direction.

Consequently, the light, having mixed polarization states/directions,emitted from the image surface 5 is changed into a singleS-polarization.

However, the stereoscopic image apparatus using the conventionalpolarizing beam splitter has the following problems.

In general, a vertical exit angle of the projector is about 15 degrees.A case in which the exit angle is 15 degrees is shown in FIG. 3. Apolarizer and a modulator are omitted from FIG. 3 for simplicity's sake.

It is assumed that the distance between a polarizing beam splitter and areflective member 16 and the distance between the polarizing beamsplitter and another reflective member 16 are h1 and h2, respectively,and the distances between the respective reflective member 16 and 17 anda screen 18 are L1 and L2, respectively.

In this case, an angle θ1 between the fight reflected by the reflectivemember 16 and an optical axis of the light emitted from the projector isTAN−1(h1/L1) and an angle θ2 between the light reflected by thereflective member 17 and the optical axis of the light emitted from theprojector is TAN−1(h2/L2).

Reference numeral 161 indicates the light reflected by the reflectivemember 16 and reference numeral 171 indicates the light reflected by thereflective member 17.

Distortion of an image on the screen 18 due to the angles θ1 and θ2 isas follows. FIG. 4 is an enlarged view showing part (A) of FIG. 3.

Referring to FIG. 4, reference numeral 161 indicates the light reflectedby the reflective member 16 and reference numeral 171 indicates thelight reflected fey the reflective member 17.

In addition, reference numeral 162 indicates an image-forming surface ofthe light reflected by the reflective member 16 and reference numeral172 indicates an image-forming surface of the light reflected by thereflective member 17.

On the assumption that the height of the screen 18 is H, a heightdifference d1 between the image-forming surface of the light reflectedby the reflective member 16 and the image on the screen 18 and a heightdifference d2 between the image-forming surface of the light reflectedby the reflective member 17 and the image on the screen 18 are expressedas follows.d1=H TAN(θ1),d2=H TAN(θ2)

Consequently, the beams reflected by the reflective members 16 and 17form images on the image-forming surface with a distance differenceΔ=(H/2) {TAN (θ1)+TAN (θ2)}.

In a case in which h1≈h2=340 mm, L1≈L2=1500 mm, and H=8500 mm, θ1≈θ2=1.3degrees and, therefore, Δ=193 mm.

This means that the tight reflected by the reflective member 16 and thelight reflected by the reflective member 17 deviate from each other onthe image-forming surface by a maximum of 193 mm. In general, the spotsize of light is several mm. As the distance from the center of thescreen 18 is increased, therefore, the image is less visible, whichleads to limitations in use.

DISCLOSURE Technical Problem

An object of the present invention devised to solve the problem lies ona stereoscopic image apparatus that is capable of improving quality of astereoscopic image and minimizing loss of optical energy.

Technical Solution

In accordance with an aspect of the present invention, the above andother objects can be accomplished by the provision of a stereoscopicimage apparatus including a polarizing beam splitter to reflect ortransmit incident light based on polarization states of the light tosplit the light into at least three different directions, a reflectivemember to reflect the light reflected by the polarizing beam splitter toa screen, at least one modulator to modulate the light reflected by thereflective member and the light transmitted through the polarizing beamsplitter, and a refractive member disposed in an advancing direction oflight to be incident upon the polarizing beam splitter and adapted torefract the light to be incident upon the polarizing beam splitter.

Advantageous Effects

According to the present invention, it is possible to overcomedeterioration in image quality and impossibility in realization of alarge screen due to misalignment of two beams on the screen, which arecaused in the conventional stereoscopic image apparatus.

That is, a path of light is divided into one path of transmitted lightand two paths of reflected light and the divided beams are combined onthe screen, thereby considerably reducing a height error of an image.

Furthermore, two polarizing beam splitters connected to each other whilebeing bent are provided such that some of incident light is reflected byand transmitted through one of the polarizing beam splitters and therest of the incident light is reflected by and transmitted through theother polarizing beam splitter. Consequently, the beams are dividedalong the respective paths, thereby achieving a precise stereoscopicimage.

Meanwhile, the refractive member is disposed in front of the polarizingbeam splitter to prevent the light from being incident upon a dimmingarea formed at the polarizing beam splitter, thereby preventing loss ofoptical energy.

That is, light incident upon the center of the refractive member isrefracted and refracted beams emit while being uniformly spaced apartfrom each other and are incident upon the polarizing beam splitter.Since the dimming area is located between the refracted beams, it ispossible to prevent the light emitted from the refractive member fromentering the dimming area.

In addition, an additional member may be disposed on the path of thetransmitted light to increase a divergence angle of the transmittedlight or an additional member may be disposed on the path of thereflected light to decrease a divergence angle of the reflected light,thereby reducing a height difference between the transmitted light andthe reflected light and thus considerably reducing an error of theimage.

In addition, the polarizing beam splitter includes two lighttransmission members connected to each other and a polarizing beamsplitting film disposed between the light transmission members.Consequently, it is possible to remove astigmatism of the lightreflected by the polarizing beam splitter and transmitted through thepolarizing beam splitter.

Meanwhile, it is possible to reduce the distance between the polarizingbeam splitter and the reflective member as compared with theconventional stereoscopic image apparatus, thereby reducing the size ofthe stereoscopic image apparatus and thus achieving a compact structureof the stereoscopic image apparatus.

It will be appreciated by persons skilled in the art that the effectsthat could be achieved with the present invention are not limited towhet has been particularly described hereinabove and other advantages ofthe present invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings.

DESCRIPTION OF DRAWINGS

FIG. 1 is a view showing a conventional polarizing beam splitting methodto obtain single polarization;

FIG. 2 is a view showing the structure of a conventional stereoscopicimage apparatus;

FIGS. 3 and 4 are side sectional views illustrating problems of theconventional stereoscopic image apparatus;

FIG. 5 is a view showing the basic structure of a stereoscopic imageapparatus according to the present invention;

FIG. 6 is a view showing paths of light in polarizing beam splitters ofthe stereoscopic image apparatus according to the present invention;

FIG. 7 is a view showing a path of light in a case in which refractivemembers are added to the stereoscopic image apparatus according to thepresent invention;

FIG. 8 is a view showing another form of the polarizing beam splitter ofthe stereoscopic image apparatus according to the present invention;

FIG. 9 is a view showing the structure of the stereoscopic imageapparatus according to the present invention in a case in which therefractive member is added to the stereoscopic image apparatus;

FIG. 10 is a view showing the structure of the stereoscopic imageapparatus according to the present invention in a case in which aplurality of different modulators is disposed in the stereoscopic imageapparatus;

FIG. 11 is a view showing the structure of the stereoscopic imageapparatus according to the present invention in a case in which a halfwave retarder is disposed in the stereoscopic image apparatus of FIG.10;

FIG. 12 is a view showing a path of light in the stereoscopic imageapparatus according to the present invention;

FIG. 13 is a side view showing a structure to correct a path oftransmitted light in the stereoscopic image apparatus according to thepresent invention; and

FIGS. 14 to 17 are side views showing structures to correct a path ofreflected light in the stereoscopic image apparatus according to thepresent invention.

BEST MODE

Hereinafter, the preferred embodiments of the present invention will bedescribed with reference to the accompanying drawings.

FIG. 5 is a view showing the basic structure of a stereoscopic imageapparatus according to the present invention.

Hereinafter, an image signal will be referred to as ‘light’ for the sakeof convenience and, therefore, the term light involves the meaning ofthe ‘image signal’.

As shown in FIG. 5, light having bean emitted from an image surface 19and passed through a projection lens 20, is incident upon polarizingbeam splitters (PBS) 21 and 22 in a state in which the light has aP-polarization and an S-polarization in a mixed state.

For the sake of convenience, the polarizing beam splitter denoted byreference numeral 21 will be referred to as a first polarizing beamsplitter and the polarizing beam splitter denoted by reference numeral22 will be referred to as a second polarizing beam splitter.

The polarizing beam splitters 21 and 22 may not be formed in a singleflat plate shape. The polarizing beam splitters 21 and 22 may be formedsuch that a section defined by the polarizing beam splitters 21 and 22are bent.

The center of the polarizing beam splitters 21 and 22 may be located onan optical axis of incident light.

The first polarizing beam splitter 21 and the second polarizing beamsplitter 22 may be connected to each other. The first polarizing beanssplitter 21 and the second polarizing beam splitter 22 may be disposedsuch that the first polarizing beam splitter 21 and the secondpolarizing beam splitter 22 face in different directions.

That is, the first polarizing beam splitter 21 and the second polarizingbeam splitter 22 may be each formed in a plate shape such that the plateshape of the first polarizing beam splitter 21 and the plate shape ofthe second polarizing beam splitter 22 are inclined in differentdirections.

In the above structure, one half of the light incident upon thepolarizing beam splitters 21 and 22 may be incident upon the firstpolarizing beam splitter 21 and the ether half of the light incidentupon the polarizing beam splitters 21 and 22 may be incident upon thesecond polarizing beam splitter 22.

The polarizing beam splitters 21 and 22 transmit a specific polarizationcomponent (a P-polarization component) and reflect another polarizationcomponent (an S-polarization component) in a direction different from adirection in which the light is transmitted to split the light in aplurality of directions.

Consequently, the P-polarization component of the light incident uponthe first polarizing beam splitter 21 is transmitted and then advancesto a screen.

On the ether hand, the S-polarization component of the light incidentupon the first polarizing beam splitter 21 is reflected and thenadvances in a first direction (in an upward direction in FIG. 5).

In addition, the P-polarization component of the light incident upon thesecond polarizing beam splitter 22 is transmitted and then advances tothe screen.

On the other hand, the S-polarization component of the light incidentupon the second polarizing beam splitter 22 is reflected and thenadvances in a second direction (in a downward direction in FIG. 5).

That is, some of the incident light is reflected and the rest of theincident light is transmitted.

The reflected light is also split. Some of the reflected light isreflected by the first polarizing beam splitter 21 and the rest of thereflected light is reflected by the second polarizing beam splitter 22.

In addition, the transmitted light is also split. Some of thetransmitted light is transmitted through the first polarizing beamsplitter 21 and the rest of the transmitted light is transmitted throughthe second polarizing beam splitter 22.

Above the first polarizing beam splitter 21 and the second polarizingbeam splitter 22 are respectively provided reflective members 23 and 24,such as mirrors, which are spaced apart from the first polarizing beamsplitter 21 and the second polarizing beam splitter 22, respectively.

Representative examples of the reflective members 23 and 24 may be themirrors. However, the present invention is not limited thereto. Thereflective members 23 and 24 may be constituted by all elements that arecapable of embodying a function to reflect light.

The reflective member denoted by reference numeral 23 will be referredto as a first reflective member and the reflective member denoted byreference numeral 24 will be referred to as a second reflective member.

The light reflected by the first polarizing beam splitter 21 and thefirst reflective member 23 and the light reflected by the secondpolarizing beam splitter 22 and the second reflective member 24 eachhave the S-polarization. The light reflected by the first polarizingbeam splitter 21 and the first reflective member 23 and the lightreflected by the second polarizing beam splitter 22 and the secondreflective member 24 advance to the screen and are then combined witheach other on the screen.

The beams reflected and then advancing in two directions may be providedto divide the section of the incident light into two equal parts. Thebeams reflected and then advancing in the two directions have the samepolarization component.

Meanwhile, the beams transmitted through the first polarizing beamsplitter 21 and the second polarizing beam splitter 22 advance to thescreen along an optical axis while having the P-polarization component.

In the above structure, one half of the light having passed through theprojection lens 20 may reach the first polarizing beam splitter 21 andmay be then reflected by the first polarizing beam splitter 21 or may betransmitted through the first polarizing beam splitter 21 and the otherhalf of the light transmitted through the projection lens 20 may reachthe second polarizing beam splitter 22 and may be then reflected by thesecond polarizing beam splitter 22 or may be transmitted through thesecond polarizing beam splitter 22.

In a case in which images having the same size are projected on thescreen, therefore, it is possible to considerably reduce the distancebetween the polarizing beam splitters 21 and 22 and the reflectivemembers 23 and 24 as compared with the conventional stereoscopic imageapparatus, which means that it is possible to reduce the size of thestereoscopic image apparatus.

In a case in which the distance between the polarizing beam splitters 21and 22 and the reflective members 23 and 24 of the stereoscopic imageapparatus according to the present invention is equal to the distancebetween the polarizing beam splitters and the reflective members of theconventional stereoscopic image apparatus, on the other hand, the sizeof the image projected on the screen in the stereoscopic image apparatusaccording to the present invention may be considerably greater than thesize of the image projected on the screen in the conventionalstereoscopic image apparatus based on the above structure.

The reason that the size of the stereoscopic image apparatus may bereduced as described above will hereinafter be described in detail.

FIG. 6 shows paths of light transmitted through the first polarizingbeam splitter 21 and the second polarizing beam splitter 22.

As shown in FIG. 6, light, having a diameter D, incident upon the firstpolarizing beam splitter 21 and the second polarizing beam splitter 22is refracted when the light is transmitted through the first polarizingbeam splitter 21 and the second polarizing beam splitter 22.

In this case, most of the transmitted light is transmitted through thefirst polarizing beam splitter 21 and the second polarizing beamsplitter 22 and moves behind the first polarizing beam splitter 21 andthe second polarizing beam splitter 22. However, center light (lighthaving a diameter d) enters the first polarizing beam splitter 21 andthe second polarizing beam splitter 22 and then converges upon onepoint.

Consequently, the light having the diameter d does not reach the screenbut becomes extinct.

That is, light is incident upon a bent portion defined between the firstpolarizing beam splitter 21 and the second polarizing beam splitter 22and is then concentrated on one point to form a dimming area (DA).

Some of the light having passed through the polarizing beam splitters 21and 22 passes through the dimming area (DA). At this time, energy of thelight is reduced. Consequently, luminous intensity on the screen islowered with the result that the overall area of the screen isrelatively darkened.

Therefore, it is necessary to provide a correction method that iscapable of solving the above problem.

FIG. 7 shows a structure related to such a correction method.

As shown in FIG. 7, refractive members 25 and 26 having a refractiveindex and thickness similar to those of the first polarizing beamsplitter 21 and the second polarizing beam splitter 22 are provided.

The refractive members 25 and 26 may be each formed in a plate shape.However the present invention is not limited thereto.

The refractive member 25 corresponding to the first polarizing beamsplitter 21 will be referred to as a first refractive member and therefractive member 26 corresponding to the second polarizing beamsplitter 22 will be referred to m a second refractive member.

The shape of the first refractive member 25 is similar to that of thefirst polarizing beam splitter 21 and the shape of the second refractivemember 26 is similar to that of the second polarizing beam splitter 22.

That is, the first refractive member 25 is located above the opticalaxis and the second refractive member 26 is located under the opticalaxis. The first refractive member 25 and the second refractive member 26are connected to each other. A bent portion is formed at the center ofthe first refractive member 25 and the second refractive member 26.

The first refractive member 25 and the second refractive member 26 mayface the first polarizing beam splitter 21 and the second polarizingbeam splitter respectively, in a symmetrical fashion.

The first refractive member 25 and the second refractive member 26 areinclined in different directions in a state in which the firstrefractive member 25 and the second refractive member 26 are connectedto each other.

In the above structure, paths of beams are formed as follows.

The beams incident upon the refractive members 25 and 26 are refractedwith the result that paths of the beams are changed. The beams move tothe polarizing beam splitters 21 and 22.

At this time, an empty area (EA), though which beams do not pass, isformed between the center of the refractive members 25 and 26 and thepolarizing beam splitters 21 and 22 since the center of the refractivemembers 25 and 26 is bent.

The incident path of the light incident upon the dimming area (DA) shownin FIG. 6 corresponds to the empty area (EA) shown in FIG. 7. Since thelight does not advance to the empty area (EA) any longer due torefraction of the light by the refractive members 25 and 26, the lightis not incident upon the dimming area (DA) any longer. Consequently, itis possible to prevent loss of the light due to light extinction.

FIG. 8 is a view showing a method of reducing astigmatism which mayoccur in the polarizing beam splitter.

The first polarizing beam splitter 21, the first refractive member 25,and the first reflective member 23 are shown in FIG. 8. However,descriptions of the first polarizing beam splitter 21, the firstrefractive member 25, and the first reflective member 23 are equallyapplied to the second polarizing beam splitter 22, the second refractivemember 26, and the second reflective member 24.

When light having passing through the first refractive member 25 reachesthe first polarizing beam splitter 21, a P-polarization is transmittedthrough the first polarizing beam splitter 21 and an S-polarization isreflected by the overall surface of the first polarizing beam splitter21 and then advances to the first reflective member 23.

At this time, the length of the path of the transmitted light isincreased by a thickness T of the first polarizing beam splitter 21 ascompared with the length of the path of the reflected light. This isbecause the reflected light does not move in the first polarizing beamsplitter 21 and is then reflected but is reflected by the surface of thefirst polarizing beam splitter 21, whereas the transmitted fight passesthrough the first polarizing beam splitter 21.

In this case, astigmatism of the light may occur due to the differencein length of the path between the reflected light and the transmittedlight.

In order to correct such astigmatism, it is necessary to equalize thelength of the light reflected by the first polarizing beam splitter 21and the length of the light transmitted through the first polarizingbeam splitter 21.

Consequently, the first polarizing beam splitter 21 is formed bycombining two light transmission members 211 and 212 having the samethickness. A polarizing beam splitting film 213 is disposed between thelight transmission members 211 and 212.

On the assumption that the thickness of the first polarizing beamsplitter 21 is T and the thickness of each of the light transmissionmembers 211 and 212 is t, T=2t (the thickness of the polarizing beamsplitting film being ignored).

For the sake of convenience, it is assumed that the thickness of thelight transmission member 211 located on the front side is t1 and thethickness of the light transmission member 212 located on the rear sideis t2.

The P-polarization of the incident light passes through the front sidelight transmission member 211, the polarizing beam splitting film 213,and the rear side light transmission member 212. At this time, thelength of the path of the transmitted light in the first polarizing beamsplitter 21 is t1+t2.

On the other hand, the S-polarization of the incident light passesthrough the front side light transmission member 211, reaches thepolarizing beam splitting film 213 and is reflected by the polarizingbeam splitting film 213, and then passes through the front side lighttransmission member 211.

At this time, the length of the path of the reflected light in the firstpolarizing beam splitter 21 is t1+t1. Since t1=t2 as described above,the length of the path of the reflected light and the length of the pathof the transmitted light are equal. Consequently, it is possible toprevent the occurrence of astigmatism.

The incident angle, the transmission angle, and the reflection angle ofthe reflected light and the transmitted light are not exactly 0. Sincethe first polarizing beam splitter 21 and the light transmission members211 and 212 constituting the first polarizing beam splitter 21 are verythin, however, the change in length of the paths due to the angles maybe ignored.

FIG. 9 is a view showing basic construction of a polarizing beamsplitting method according to the present invention.

The section of the reflected S-polarization is divided into two equalparts. As a result, the distance between an optical axis of theprojection lens 20 and the first reflective member 23 and the distancebetween the optical axis of the projection lens 20 and the secondreflective member 24 are reduced by half. For example, the distancebetween an optical axis of the projection lens 20 and the firstreflective member 23 and the distance between the optical axis of theprojection lens 20 and the second reflective member 24 may be 75 mm.

The above distance in the polarizing beam splitting method according tothe present invention is equivalent to ¼ the distance, which is 340 mm,in the conventional polarizing beam splitting method shown in FIG. 2,which means that angle errors θ1 and θ2 with the image-forming surfaceon the screen 18 shown in FIG. 2 are reduced to about ¼ those when theconventional method is used.

Next, a description will be given of a case in which the structure shownin FIG. 9 is applied to a stereoscopic image apparatus having enhancedbrightness.

Referring to FIG. 10, the S-polarization reflected by the firstreflective member 23 and the second reflective member 24 is modulated bya first modulator 27 a and a third modulator 27 c, respectively.

On the other hand, the P-polarization transmitted through the firstpolarizing beam splitter 21 and the second polarizing beam splitter 22is modulated by a second modulator 27 b.

The first modulator 27 a and the third modulator 27 c are provided suchthat the first modulator 27 a and the third modulator 27 c have the samephase retardation function. The second modulator 27 b is provided suchthat the second modulator 27 b has a half wavelength phase differencefrom the first and third modulators 27 a and 27 c.

The first and third modulators 27 a and 27 c convert a state of theS-polarization according to an electric signal. For example, the firstand third modulator 27 a and 27 c convert the state of theS-polarization from a linear polarization state to a circularpolarization state.

Meanwhile, the P-polarization transmitted through the polarizing beamsplitters 21 and 22 is modulated into an S-polarization white passingthrough the second modulator 27 b. At the same time, the state of theP-polarization is modulated from a linear polarization state to acircular polarization state.

The first and third modulator 27 a and 27 c convert a state of theS-polarization from a linear polarization state to a circularpolarization state while maintaining the S-polarization. Consequently,the first and third modulator 27 a and 27 c perform a ¼ wavelength phaseretardation function.

On the other hand, the second modulator 270 converts the state of theP-polarization from a linear polarization state to a circularpolarization state (performs ¼ wavelength phase retardation function)while converting the P-polarization into an S-polarization (performing a½ wavelength phase retardation function). Consequently, the secondmodulator 27 b performs a total of ¾ wavelength phase retardationfunction.

In the embodiment shown in FIG. 10, the first to third modulators 27 ato 27 c may be separated from each other or spaced apart from eachother.

This is because, in a state in which the first modulator 27 a, thesecond modulator 27 b, and the third modulator 27 c are successivelydisposed, characteristics of phase retardation generated in the firstand third modulator 27 a and 27 c are different from those of phaseretardation generated in the second modulator 27 b.

FIG. 11 is a view showing another embodiment having another elementadded to the embodiment shown in FIG. 10.

FIG. 11 shows a structure in which a half wave retarder 28 to convertthe P-polarization transmitted through the first polarizing beamsplitter 21 and the second polarizing beam splitter 22 into anS-polarization is added to the structure shown in FIG. 10.

That is, the half wave retarder 28 is disposed at the rear of the firstand second polarizing beam splitters 21 and 22 and is disposed in frontof the second modulator 27 b.

In other words, the half wave retarder 28 is disposed between the firstand second polarizing beam splitters 21 and 22 and the second modulator27 b.

In the above structure, the light having passed through the half waveretarder 28 and the light reflected by the first and second reflectivemembers 23 and 24 have characteristics of the same polarization, i.e.the S-polarization.

Consequently, it is possible to convert the polarizations from a linearpolarization state to a circular polarization state using a singlelarge-sized modulator instead of the first, second, and third modulators27 a, 27 b, and 27 c. The single large-sized modulator may retard thephase of incident light by a ¼ wavelength to convert the light from alinear polarization state to a circular polarization state.

Meanwhile, although not shown, the half wave retarder 28 may be disposedbetween the first reflective member 23 and the first modulator 27 aand/or between the second reflective member 24 and the third modulator27 c.

In a case in which both a polarization moving along a reflection pathand a polarization moving along a transmission path reach the screen,the polarizations must be changed into a single polarization (aP-polarization or an S-polarization).

In a case in which the half wave retarder 28 is disposed on thetransmission path, therefore, the polarizations reaching the screen mayform an image on the screen in an S-polarization state.

On the other hand, in a case in which the half wave retarder 28 isdisposed on the reflection path, the polarizations reaching the screenmay form an image on the screen in a P-polarization state.

According to the present invention as described above, the number ofpaths of beams projected on the screen in an overlapping fashion is 3.

That is, the paths of beams include a first path along which light istransmitted through the first polarizing beam splitter 21 and the secondpolarizing beam splitter 22 and is then projected on the screen, asecond path along which light is reflected by the first polarizing beamsplitter 21 and the first reflective member 23 and is then projected onthe screen, and a third path along which light is reflected by thesecond polarizing beam splitter 22 and the second reflective member 24and is then projected on the screen.

Next, a description will be given of a method of overcoming a differencebetween the image-forming surface of the light reflected by the firstpolarizing beam splitter 21 and the second polarizing beam splitter 22and the image-forming surface of the light transmitted through the firstpolarizing beam splitter 21 and the second polarizing beam splitter 22to provide images having the same size on the screen.

FIG. 12 shows a height difference Δ between image-forming surfaces oflight primarily reflected by the first polarizing beam splitter 21 andthe second polarizing beam splitter 22 and secondarily reflected by thefirst reflective member 23 and the second reflective member 24 andimage-forming surfaces of light transmitted through the first polarizingbeam splitter 21 and the second polarizing beam splitter 22.

Reference numeral 219 indicates the image-forming surface of the lighttransmitted through the first polarizing beam splitter 21 and referencenumeral 229 indicates the image-forming surface of the light transmittedthrough the second polarizing beam splitter 22.

Reference numeral 239 indicates the image-forming surface of the lightreflected by the first reflective member 23 and reference numeral 249indicates the image-forming surface of the light reflected by the secondreflective member 24.

The image-forming surfaces 239 and 249 of the beams moving alongreflection paths are located in front of the wage-forming surfaces 219and 229 of the beams moving along transmission paths. The heightdifference Δ is generated due to such a difference in position.

The height difference Δ may be reduced using the following four methods.

A first method is to increase a divergence angle of the lighttransmitted through the first polarizing beam splitter 21 and the secondpolarizing beam splitter 22 using a lens 29 as shown in FIG. 13.

The lens may have characteristics of a concave lens to increase thedivergence angle of the light.

In this method, a light path 299 after correction is performed by thelens 29 diverges more than a light path 298 before correction isperformed by the lens 29 with the result that the size of an image onthe screen is increased.

Referring to FIG. 13, a transmission path indicated by a solid lineindicates the path 298 before correction is performed by the lens 29 anda transmission path indicated by a dotted line indicates the path 299after correction is performed by the lens 29.

It can be seen that the path indicated by the dotted line diverges morethan the path indicated by the solid line.

As a result, the size of an image formed on the screen by the beamsmoving along the transmission paths becomes equal to the size of animage formed on the screen by the beams moving along the reflectionpaths, whereby the above-described height difference Δ may be removed.

At this time, it should be noted that the lens 29 must be disposedbetween the two reflection paths such that the beams moving along thereflection paths do not interfere with the lens 29.

A second method of removing the height difference Δ is to dispose tenses30 and 31 to reduce divergence angles of the beams on the reflectionpaths as shown in FIG. 14.

The lenses 30 and 31 may have characteristics of convex lenses todecrease the divergence angles of the beams to a certain extent.

The lenses 30 and 31 may be disposed adjacent to the first reflectivemember 23 and the second reflective member 24 in a state in which thetenses 30 and 31 are located on paths along which the beams reflected bythe first reflective member 23 and the second reflective member 24advance.

In this method, fight paths 309 and 319 after correction is performed bythe lenses 30 and 31 diverge less than light paths 308 and 318 beforecorrection is performed by the lenses 30 and 31 with the result that thesize of an image on the screen is decreased.

Referring to FIG. 14, reflection paths indicated by solid lines indicatethe paths 308 and 318 before correction is performed by the lenses 30and 31 and reflection paths indicated by dotted lines indicate the paths309 and 319 after correction is performed by the lenses 30 and 31.

It can be seen that the paths indicated by the dotted lines diverge lessthan the paths indicated by the solid lines.

As a result, the size of an image formed on the screen by the beamsmoving along the reflection paths becomes equal to the size of an imageformed on the screen by the beams moving along the transmission paths,whereby the above-described height difference Δ may be removed.

At this time, it should be noted that the lenses 30 and 31 must deviatefrom the transmission paths such that the beams moving along thetransmission paths do not interfere with the lenses 30 and 31.

On the other hand, it is possible to use a method of correcting paths ofbeams using plates or prisms 32 and 33 to reduce divergence angles ofthe beams as shown in FIG. 15 instead of using the correction methodusing the lenses 30 and 31 as shown in FIG. 14.

This is a third method of removing the height difference Δ.

The plates or prisms 32 and 33 may have characteristics of convex lensesto decrease the divergence angles of the beams to a certain extent.

The plates or prisms 32 and 33 may be disposed adjacent to the firstreflective member 23 and the second reflective member 24 in a state inwhich the plates or prisms 32 and 33 are located on paths along whichthe beams reflected by the first reflective member 23 and the secondreflective member 24 advance.

In this method, light paths 329 and 339 after correction is performed bythe plates or prisms 32 and 33 diverge less than light paths 328 and 338before correction is performed by the plates or prisms 32 and 33 withthe result that the size of an image on the screen is decreased.

Referring to FIG. 15, reflection paths indicated by solid lines indicatethe paths 328 and 338 before correction is performed by the plates orprisms 32 and 33 and reflection paths indicated by dotted lines indicatethe paths 329 and 339 after correction is performed by the plates orprisms 32 and 33.

It can be seen that the paths indicated by the dotted lines diverge lessthan the paths indicated by the solid lines.

As a result, the size of an image formed on the screen by the beamsmoving along the reflection paths becomes equal to the size of an imageformed on the screen by the beams moving along the transmission paths,whereby the above-described height difference Δ may be removed.

At this time, it should be noted that the plates or prisms 32 and 33must deviate from the transmission paths such that the beams movingalong the transmission paths do not interfere with the plates or prisms32 and 33.

A fourth method of removing the height difference Δ is to use reflectivemember-prism assemblies (mirror-prism assemblies) 34 and 35 as shown inFIG. 16.

The reflective member-prism assemblies 34 and 35 are configured suchthat the lenses 30 and 31 or the plates or prisms 32 and 33 shown inFIG. 14 or 15 are easily and conveniently spaced apart from thereflective members.

The reflective member-prism assemblies 34 and 35 reduce divergenceangles of beams.

The reflective member-prism assemblies 34 and 35 may be located on pathsalong which the beams reflected by the first polarizing beam splitter 21and the second polarizing beam splitter 22 advance.

In this method, light paths 349 and 359 after correction is performed bythe reflective member-prism assemblies 34 and 35 diverge less than lightpaths 348 and 358 before correction is performed by the reflectivemember-prism assemblies 34 and 35 with the result that the size of animage on the screen is decreased.

Referring to FIG. 16, reflection paths indicated fey solid linesindicate the paths 348 and 358 before correction is performed by thereflective member-prism assemblies 34 and 36 and reflection pathsindicated by dotted lines indicate the paths 349 and 359 aftercorrection is performed by the reflective member-prism assemblies 34 and35.

It can be seen that the paths indicated by the dotted lines diverge lessthan the paths indicated by the solid lines.

As a result, the size of an image formed on the screen by the beamsmoving along the reflection paths becomes equal to the size of an imageformed on the screen by the beams moving along the transmission paths,whereby the above-described height difference Δ may be removed.

Meanwhile, it is possible to provide the same effect even when using apolarizing beam splitter constituted by a prism 38 having two polarizingbeam splitting surfaces 36 and 37 as shown in FIG. 17.

That is, the polarizing beam splitter may include the polarizing beamsplitting surfaces 36 and 37 connected to each other while beinginclined and the prism 38.

A polarization having a specific direction (e.g. a P-polarization) istransmitted through the polarizing beam splitting surfaces 36 and 37.

On the other hand, a polarization having another direction (e.g. anS-polarization) is reflected by the polarizing beam splitting surfaces36 and 37 and the path of the reflected light is corrected by the prism38.

That is, the path of the reflected light is corrected such that the pathof the reflected light diverges less.

Meanwhile, refractive members 39 and 40 may be disposed in front of thepolarizing beam splitter. The function and structure of the refractivemembers 39 and 40 are the same as those of the refractive members 25 and26 shown in FIG. 7.

Accordingly, a description of the refractive members 39 and 40 will feereplaced by a description of the refractive members 25 and 26 shown inFIG. 7 and, therefore, will be omitted.

According to the present invention as described above, it is possible toreduce the difference between the advancing path of the reflected lightand the advancing path of the transmitted light, thereby obtaining ahigh-quality stereoscopic image.

In addition, it is possible to reduce the distance among the elements ofthe stereoscopic image apparatus as compared with the conventionalstereoscopic image apparatus, thereby reducing the overall size of thestereoscopic image apparatus.

Those skilled in the art will appreciate that the present invention maybe embodied in other specific forms than those set forth herein withoutdeparting from the spirit and essential characteristics of the presentinvention. The above description is therefore to be construed in allaspects as illustrative and not restrictive. The scope of the inventionshould be determined by reasonable interpretation of the appended claimsand all changes coming within the equivalency range of the invention areintended to be within the scope of the invention.

What is claimed is:
 1. A stereoscopic image apparatus for projecting astereoscopic image towards an image-forming surface, the stereoscopicimage apparatus comprising: a polarization beam splitter adapted tosplit an incident image light into a transmitted light having a firststate of polarization, and first and second reflected lights having asecond state of polarization, the second state being different from thefirst state, wherein the polarization beam splitter has at least twoplates joined to each other, and a junction of the two plates is locatedon a path of the incident image light; first and second reflectivemembers configured to modify paths of the first and the second reflectedlights so that the transmitted light and the first and the secondreflected lights collectively form the stereoscopic image; wherein thestereoscopic image is formed by overlapping of a first image formed fromthe transmitted light and a second image formed from the first andsecond reflected lights, wherein the second image is formed by combiningthe first and second reflected lights, the second image having at leastone non-overlapped area; and first, second and third polarizationmodulators configured to selectively switch the polarization states ofthe transmitted light and the first and the second reflected lightsbetween the first and the second states of polarization, wherein thefirst, the second and the third polarization modulators are controlledto selectively switch the polarization state of the transmitted lightand the first and the second reflected lights to have the same state ofpolarization.
 2. The apparatus according to claim 1, wherein thepolarization beam splitter comprises a first polarization beam splitterand a second polarization beam splitter having a form of the two plates,respectively, wherein the first polarization beam splitter and thesecond polarization beam splitter are joined to each other to have achevron shape.
 3. The apparatus according to claim 1, wherein thepolarization beam splitter comprises a first polarization beam splitterand a second polarization beam splitter having a form of the two plates,respectively, and wherein the junction between the first polarizationbeam splitter and the second polarization beam splitter forms an edgeplaced on the path of the incident image light.
 4. The apparatusaccording to claim 1, wherein the two plates are symmetrical relative tothe path of the incident image light.
 5. The apparatus according toclaim 1, further comprising: a lens placed on the path of thetransmitted light transmitted through the polarization beam splitter,wherein the lens is adapted to increase a divergence angle of thetransmitted light.
 6. The apparatus according to claim 1, wherein thefirst state of polarization is P-polarization and the second state ofpolarization is S-polarization.
 7. The apparatus according to claim 1,wherein the first and the third polarization modulators have the samephase retardation function, and wherein the second polarizationmodulator has a half wavelength phase difference from the first and thethird polarization modulators.
 8. The apparatus according to claim 1,further comprising: a retarder to make the transmitted light, and thefirst and the second reflected light have the same state of polarizationfor forming the stereoscopic image.
 9. The apparatus according to claim1, further comprising: at least two plates or lenses provided on a pathof light respectively reflected by the first and second reflectivemembers to decrease a divergence angle of the light reflected by thefirst and the second reflective members to correct the path of thelight.
 10. The apparatus according to claim 1, wherein the firstreflective member comprises a first mirror and the second reflectivemember comprises a second mirror.
 11. The apparatus according to claim1, wherein the first reflective member comprises a first prism and thesecond reflective member comprises a second prism.
 12. The apparatusaccording to claim 1, wherein the first state of polarization and thesecond state of polarization are orthogonal to each other.
 13. Astereoscopic image apparatus for projecting a stereoscopic image towardsan image-forming surface, the stereoscopic image apparatus comprising: apolarization beam splitter adapted to split an incident image light intoa transmitted light having a first state of polarization, and first andsecond reflected lights having a second state of polarization, thesecond state being different from the first state, wherein thepolarization beam splitter has at least one prism and first and secondpolarization beam splitting surfaces arranged at an angle to each other,and a junction of the first and second polarization beam splittingsurfaces is located on a path of the incident image light; first andsecond reflective members configured to modify paths of the first andthe second reflected lights so that the transmitted light and the firstand the second reflected lights collectively form the stereoscopicimage, wherein the stereoscopic image is formed by overlapping of afirst image formed from the transmitted light and a second image formedfrom the first and second reflected lights, and wherein the second imageis formed by combining the first and second reflected lights, the secondimage having at least one non-overlapped area; and first, second andthird polarization modulators configured to selectively switch thepolarization states of the transmitted light and the first and thesecond reflected lights between the first and the second states ofpolarization, wherein the first, the second and the third polarizationmodulators are controlled to selectively switch the polarization statesof the transmitted light and the first and the second reflected lightsto have the same state of polarization.
 14. The apparatus according toclaim 13, wherein the incident image light sequentially passes throughthe at least one prism and one of the first and second polarization beamsplitting surfaces.
 15. A stereoscopic image apparatus for projecting astereoscopic image towards an image-forming surface, the stereoscopicimage apparatus comprising: a polarization beam splitter adapted tosplit an incident image light into a transmitted light having a firststate of polarization, and first and second reflected lights having asecond state of polarization, the second state being different from thefirst state, wherein the polarization beam splitter has a first and asecond polarization beam splitting surface that are connected in ajunction and disposed in an advancing direction of the incident imagelight to reflect respective portions of the incident image light havingthe second state of polarization to become the first and secondreflected lights, respectively; a refractive member disposed in a pathof the incident image light before the polarization beam splitter; firstand second reflective members configured to modify paths of the firstand the second reflected lights so that the transmitted light and thefirst and the second reflected lights are projected to collectively formthe stereoscopic image, wherein the stereoscopic image is formed byoverlapping of a first image formed from the transmitted light and asecond image formed from the first and second reflected lights, andwherein the second image is formed by combining the first and secondreflected lights, the second image having at least one non-overlappedarea; and first, second and third polarization modulators configured toselectively switch the polarization states of the transmitted light andthe first and the second reflected lights between the first and thesecond states of polarization, wherein the first, the second and thethird polarization modulators are controlled to selectively switch thepolarization states of the transmitted light and the first and thesecond reflected lights to have the same state of polarization when thestereoscopic image is formed.
 16. The apparatus according to claim 15,wherein the refractive member is a glass plate.
 17. The apparatusaccording to claim 16, wherein the glass plate is adjacent to thepolarization beam splitter.
 18. The apparatus according to claim 16,wherein the glass plate is bonded to the polarization beam splitter. 19.The apparatus according to claim 15, wherein the polarization beamsplitter comprises three prisms.
 20. The apparatus according to claim15, wherein first and second polarization beam splitting surfaces arearranged at an angle to each other, and a junction of the first andsecond polarization beam splitting surfaces is located on a path of theincident image light.
 21. The apparatus according to claim 15, wherein afirst retarder is disposed on the first reflected light path and asecond retarder is disposed on the second reflected light path.
 22. Astereoscopic image apparatus for projecting a stereoscopic image towardsan image-forming surface, the stereoscopic image apparatus comprising: apolarization beam splitter adapted to split an incident image light intoa transmitted light having a first state of polarization, and first andsecond reflected lights having a second state of polarization, thesecond state being different from the first state, wherein thepolarization beam splitter has at least two plates joined to each other,and a junction of the two plates is located on a path of the incidentimage light; first and second reflective members configured to modifypaths of the first and the second reflected lights so that thetransmitted light and the first and the second reflected lights areprojected to collectively form a stereoscopic image, wherein thestereoscopic image is formed by overlapping of a first image formed fromthe transmitted light and a second image formed from the first andsecond reflected lights, and wherein the second image is formed bycombining the first and second reflected lights, the second image havingat least one non-overlapped area; and a polarization modulatorconfigured to selectively switch the polarization states of thetransmitted light and the first and the second reflected lights betweenthe first and the second states of polarization, wherein thepolarization modulator is controlled to selectively switch thepolarization state of the transmitted light and the first and the secondreflected lights to have the same state of polarization where thestereoscopic image is formed.
 23. The apparatus according to claim 22,wherein the polarization modulator comprises first, second and thirdpolarization modulators configured to selectively switch thepolarization states of the transmitted light and the first and thesecond reflected lights between the first and the second states ofpolarization.
 24. The apparatus according to claim 22, wherein threepaths of light are projected.
 25. The apparatus according to claim 22,wherein a first retarder is disposed on the first reflected light pathand a second retarder is disposed on the second reflected light path.26. The apparatus according to claim 25, wherein the first retarder isdisposed on the first reflected light path before the polarizationmodulator, and the second retarder is disposed on the second reflectedlight path before the polarization modulator.
 27. The apparatusaccording to claim 25, wherein the first retarder is disposed on thefirst reflected light path after the polarization modulator, and thesecond retarder is disposed on the second reflected light path after thepolarization modulator.